ISEE Upper Level Math : How to find the radius of a sphere

Study concepts, example questions & explanations for ISEE Upper Level Math

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Example Questions

Example Question #1 : How To Find The Radius Of A Sphere

A wooden ball has a surface area of .

What is its radius?

Possible Answers:

Cannot be determined from the information provided

Correct answer:

Explanation:

A wooden ball has a surface area of .

What is its radius?

Begin with the formula for surface area of a sphere:

Now, plug in our surface area and solve with algebra:

Get rid of the pi

Divide by 4

Square root both sides to get our answer:

 

Example Question #2 : How To Find The Radius Of A Sphere

There is a perfectly spherical weather balloon with a surface area of  , what is its radius?

Possible Answers:

Correct answer:

Explanation:

There is a perfectly spherical weather balloon with a surface area of  , what is its radius?

Begin with the formula for surface area of a sphere:

Now, set it equal to the given surface area and solve for r:

First divide both sides by .

Then square root both sides to get our answer:

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